Casters are commonly attached to transport vehicles, such as carts, trailers, trucks, or dollies, and allow for rolling movement of the transport vehicle along a ground surface. Casters generally include a horn, also referred to as a yoke, having a pair of legs that extend downwardly and support a caster wheel that rolls along the ground surface. Casters may be classified as light-duty or heavy-duty, stem-style or plate-style, swivel or rigid, and kingpin or kingpinless, for example.
A caster is considered light-duty or heavy-duty depending generally on the magnitude of the load it is designed to support with a caster wheel. Caster wheels come in a large variety of sizes, measured both by the width of the wheel tread and by its diameter. Heavy-duty casters are generally fitted with larger diameter wheels and wider tread widths than lighter duty casters. Household furniture normally features lighter duty casters, with smaller and narrower wheels. In industrial applications, vehicles designed for transporting heavy loads feature heavy-duty casters with wider and larger diameter wheels.
Casters are generally attached to the support vehicle by either a stem or a mounting plate. Stem casters include a vertical stem, or stud, that extends upwardly from the horn and is configured to attach the caster to a vehicle. The stem is inserted into a hole or channel provided on the vehicle, such as an office chair or other furniture. In contrast, plate casters include a caster mounting plate for attaching the caster to a surface, such as a bottom surface, of the transport vehicle. Plate casters are generally used for heavy-duty applications, while stem casters are more common for light-duty applications.
Casters may be permitted to rotate about their vertical axis (termed “swivel”), or they may be fixed or restricted (termed “rigid”). Swivel casters include a horn base that is rotatably coupled with the caster mounting plate or stem such that the horn and caster wheel, comprising the lower portion of a mounted caster, may swivel about the vertical axis relative to the caster mounting plate or stem. This swiveling action allows for multi-directional rolling movement, including steering or turning of the transport vehicle. In contrast, rigid casters include a horn that is rigidly attached to the caster mounting plate, such that the horn and swivel caster wheel are fixed relative to the caster mounting plate and do not rotate about the vertical axis. Transport vehicles may be fitted with one or more swivel casters and one or more rigid casters depending on the application and transport design.
Swivel casters are generally of two designs: kingpin and kingpinless. Kingpin casters are the more traditional design and include a threaded stud or bolt, referred to as a kingpin, which extends downwardly from the caster mounting plate and is insertable into a concentric hole provided on the caster horn. A nut is threaded onto the kingpin and is tightened to couple the horn to the caster mounting plate with one or more bearings between the plate and horn to allow for swiveling movement. Swivel resistance is dependent on design and fit of mating parts, bearing types, and sometimes the tightness of the nut. Kingpinless casters essentially feature a much larger diameter kingpin, and the major parts are secured by ball bearings which also permit the rotational action. The larger kingpin in the kingpinless design provides access to the top of the caster wheel through the center of the caster mounting plate, made possible by the absence of a vertical stud or bolt within the caster structure.
Transport vehicles often include swivel casters for maneuverability, for example for steering and turning the vehicle. Most transport vehicles having mounted casters include swivel casters on the operator-end of the vehicle, which is the vehicle end on which the operator pushes or pulls to move the vehicle. This operator-end generally also features a handle on which the operator may exert a pushing or pulling force for moving the vehicle. A common caster arrangement for a transport vehicle features swivel casters provided on the operator-end of the vehicle having the handle, and rigid casters provided on the vehicle end opposite the operator-end. For maximum maneuverability, a vehicle may have only swivel casters. An example of this is a common furniture dolly. Such an arrangement provides the advantage of easy maneuverability in tight spaces. However, this arrangement presents a drawback of making consistent directional control difficult along a long, straight path. To provide both tight space maneuverability and easy directional control along longer paths, swivel casters included on the vehicle may be equipped with swivel locks. Swivel locks may be engaged to prevent the caster from swiveling, thereby allowing the swivel caster to function as a rigid caster. Swivel locks may be disengaged to allow swiveling when maximum maneuverability is desired.
During use of the transport vehicle it is often desirable to brake rotation of the caster wheels, including those of any swivel casters. For example, during vehicle loading or unloading, or when parked, the operator may desire that the transport vehicle remain stationary. Accordingly, a caster may incorporate a braking system which may be engaged to apply a braking force to the caster wheel that prevents or significantly hinders rotation of the caster wheel depending on any external forces acting against the braking force, such as a horizontal pushing or pulling force on the vehicle. Traditional braking systems include a brake actuating lever or handle which may be moved by the operator's foot or hand to engage the brake. On swivel casters, the lever or handle is traditionally mounted to the rotatable horn and thus swivels with the horn relative to the caster mounting plate. In use, the horn may swivel to a position in which the brake actuating lever or handle is positioned beneath the vehicle or otherwise beyond the convenient reach of the operator. To engage the brake, the operator must then manually position the caster to reach the brake lever or handle, or adjust the vehicle to accomplish this. This activity is both inconvenient and ergonomically challenging for the operator, who may be bending over to reach the lever while simultaneously attempting to steady the vehicle or secure the load.
Accordingly, there is a need for a caster wheel braking system that addresses the challenges and drawbacks associated with swivel casters as presented above.